Simple Theoretical Model May Explain Apparent Climate Instability

The authors propose a simple theory to explain a climatic drift previously found in a series of coupled general circulation model (GCM) experiments. Their theory places the GCM results on a simple stability diagram for the thermohaline circulation in the Atlantic. It is argued that the drift is due to Stommel’s salt advection feedback and arises because the particular spinup procedure of the coupled model has in some cases resulted in an initial state on an unstable solution branch. Such drift may result from model initialization with unsuitable relaxation boundary conditions, rather than being a climatic transition that could occur in the real world.